West Nile Virus Vaccine
West Nile Virus is a member of the Flavivirus genus and is related to the tick borne encephalitis virus. Like TBE virus, WNV is transmitted by insects –mosquitoes in the case of WNV- and causes meningitis and encephalitis in humans.
First described in 1937 in Uganda, West Nile Virus was not recognized as a major epidemiologic threat for many years. Only sporadic cases were observed in Europe; however a recent outbreak in Romania caused 500 clinical cases with an almost 10 % fatality rate. In 1999, the virus reached North America for the first time, causing an epidemic of encephalitis and meningitis in New York. Subsequently, the virus has spread across the United States within four years. Today, WNV activity is observed across the continent, including Canada and Mexico. For the years 2003 and 2004, more than 12,000 cases have been reported in the US, with a fatality rate close to 4 %.
At present, no vaccine is available to protect humans from this emerging disease. Baxter is exploiting its experience in manufacturing flavivirus vaccines to also develop a vaccine against WNV infections. This will be an inactivated whole virus vaccine similar to the highly successful vaccine developed against tick-borne encephalitis infection. It is however based on use of the Vero cell platform rather than chick cells which are used for growth of the TBE virus. West Nile grows to very high titres in Vero cells and high yields of vaccine can be obtained using this cell platform. A very similar technology has also been used for development of a highly immunogenic SARS candidate vaccine and it is anticipated that this strategy has a very high chance of success for an effective West Nile vaccine development.